Pressure sensors are present in motor vehicles for the purposes of detecting an impact, such pressure sensors being located, for example, in door cavities. These cavities are in such cases not hermetically sealed, so that the air pressure in the cavities, and therefore at the pressure sensor, matches the air pressure of the atmosphere in which the vehicle is located. If the car body around this cavity is deformed as a result of an impact, then depending on the type of impact the pressure in the area of the sensor can rise or fall briefly until equalization of the pressure with the ambient atmosphere is complete.
For the purposes of detecting an impact, brief pressure fluctuations of this type are evaluated at the sensor so as, depending on the evaluation, to activate safety systems such as airbags or belt tensioners. In known systems, the pressure sensor and associated evaluation circuit, usually a microcontroller, are housed as a unit in the motor vehicle cavity, the processing unit detecting rapid pressure fluctuations as a result of an impact and sending an activation signal to a control unit controlling the safety systems.
If the sensor and the evaluation circuit are to be located spatially separate from one another, for example when one or more evaluation circuits for various sensors in the vehicle are located at a central point, the signals generated by the pressure sensors have to be transferred over line connections to the control circuits. If one takes into account here that the pressure in the event of an impact is subject to relative fluctuations of between −3% and +20% and that atmospheric air pressure can assume values between 600 mbar and 1200 mbar, then sensor values have to be transferred for pressures between 582 mbar (97% of 600 mbar) and 1440 mbar (120% of 1200 mbar). In order to be able in the event of an impact to detect the comparatively small relative fluctuations of pressure at the sensor reliably using the pressure signal, a very high resolution i.e. a precise quantization of each sampled value transferred is required if the pressure signal is being transferred digitally. This makes the transfer of pressure signals expensive and complicated.